Printing machines, such as rotary offset lithographic duplicating machines, rotary printing presses, or the like, normally include a printing couple which comprises a number of cylinders and/or rollers such as impression cylinders, master cylinders, blanket cylinders, form rollers, ductor rollers, transfer rollers, distributor rollers, regulator rollers, oscillating rollers, and the like. An ink fountain is disposed generally at the rear of the machine for feeding ink to the various rollers of the printing couple which transfers images to copy sheets. In such printing machines as rotary offset lithographic duplicating machines, a moisture fountain also is disposed adjacent the printing couple for feeding moisture to the printing couple.
A typical moisture feeding system includes a moisture fountain with a fountain roller for picking up moisture from the fountain. The moisture is fed to a master cylinder from the fountain roller to a ductor roller, from the ductor roller to a distributor roller, from the distributor roller to a form roller, and, finally, from the form roller to the master cylinder. The moisture transfer is accomplished through surface contact between the peripheral surfaces of the respective rollers. The ductor roller reciprocates bodily in an arc between the fountain roller and the distributor roller and, therefore, intermittently rotates and consequently is not directly affected by down-line rotation of the master cylinder. On the other hand, the distributor roller is in continuous surface contact with the form roller which, in turn, is in surface contact with the master cylinder. The master cylinder actually drivingly rotates the form roller through surface contact.
A continuing problem with moisture systems of the character described is to maintain, as close as possible, equal surface speed between the master cylinder and the form roller and between the form roller and the distributor roller. Any slippage, particularly abrupt slippage, results in what is termed in the art "skid marks" in the moisture and/or ink film which is transferred to the copy sheets and which results in poor copy quality.
This problem is magnified when considering that a typical master cylinder does not have a cylindrical surface, a full 360.degree. about the periphery of the cylinder. A "gap", which actually is a recessed area of the cylindrical surface, is provided for mounting various hardware for holding or clamping the master onto the peripheral surface of the master cylinder. When this gap rotates into juxtaposition with the form roller, there no longer is any surface contact between the master cylinder and the form roller and, consequently, the surface of the cylinder does not rotatably drive the form roller during this rotational increment. Consequently, it has become conventional to provide gears between the master cylinder and the form roller, the gears having lost motion means built into them. In other words, when the gap in the master cylinder becomes rotatingly juxtaposed with the form roller, the gears take over to rotate the form roller during an increment of rotation equal to the arc of the gap and, when the cylindrical surface of the master cylinder again engages the form roller, the lost motion means in the gears allows the master cylinder to surface drive the form roller until the gap again becomes juxtaposed with the form roller.
Because the above-described gear train between the master cylinder and the form roller is only intermittently effective, the gear train cannot be used to rotate the distributor roller. Therefore, in order to control the rotation of the distributor roller, electronic sensors have been used to monitor the speed of rotation of the distributor roller. Such sensor monitoring systems must be continuously maintained and calibrated and repeatedly have timing problems. Such systems often provide too tight of a control and often result in intermittent variances in surface speed between the distributor roller and the form roller.
This invention is directed to solving the above problems by a very simple drive system between the distributor roller and the form roller which is totally independent of the lost motion drive system between the form roller and the master cylinder and which obviates all of the maintenance, monitoring and timing problems of conventional systems described above.